Most PCs don't blow air in, they blow it out, and the air inlet is well away
from the power supply block. This tends to blow dust *out* of the innards
and seems to work well, without the use of a filter. Of course, I don't know
whether you can do that with your product.
 
With best wishes DESIGN IT IN! OOO - Own Opinions Only
 <http://www.jmwa.demon.co.uk/> www.jmwa.demon.co.uk J M Woodgate and
Associates Rayleigh England
 
Sylvae in aeternum manent.
 
From: Kunde, Brian [mailto:brian_ku...@lecotc.com] 
Sent: Monday, September 19, 2016 5:43 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Risk Assessment of Air Filter
 
I seek advice and opinions from fellow safety minded people.
 
Our typical product has a metal chassis which is constructed as a Fire
Enclosure (laboratory equipment 61010-1). On the back is a cutout for a
cooling fan/blower mounted in the cutout. The fan is 24Vdc, certified by
several safety agencies, and has a finger guard.  This is typical
configuration on most electronics.
 
Now, our customers want us to install an externally changeable Air Filter on
the outside surface of our instrument where the fan is mounted to filter
dust particles from the incoming air. We already perform Blocked Vent and
Stalled Fan tests to insure no hazards are caused from the rise in internal
temperatures.  
 
But what type of Fault Testing or Risk assessment needs to be done regarding
the filter?  With the filter removed, the instrument passes the construction
requirements for a Fire Enclosure. But with the filter installed and because
of its close proximity to the fan/blower;
1.       does this filter have to meet Flammability requirements? Does the
filters have to be certified (expensive)? UL 94 HF-1?, UL 94 HF-2?, UL 900?
How are these ratings/certifications viewed outside of North America?  Will
they have to meet local requirements??
2.      If the fan/blower is certified and limited energy circuit does the
filter have to have any kind of rating or certification? In other words,
with a certified fan/blower, do I have to consider the fault condition of
the fan failing in a way where it could catch the filter on fire?  
3.      How is a fault and/or risk assessment performed on an air filter? 
4.      Are we responsible to consider the hazards from a burning filter
when it is dirty? How would we know what type of contaminates might collect
in a filter?  
5.      If the filter we provide is UL 94 HF-1 and UL 900 rated/certified,
what would stop our customer from replacing it with whatever filter they
wanted? Are we responsible to include a warning label and statements in the
manual regarding this?  Example, "Use only Air Filter part number XYZ". 
6.      Any other suggestions or issues that we are not considering?  
 
Thanks in advance. Have a nice day.

The Other Brian
  _____  


LECO Corporation Notice: This communication may contain confidential
information intended for the named recipient(s) only. If you received this
by mistake, please destroy it and notify us of the error. Thank you. 

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